There are lots of organisms that don't have a brain, but can still communicate. Bacteria coordinate their growth, plants signal distress and lure insects in with scents and coloring. Now, researchers have listened in on some of the communication going on in a coral reef, and found that the organisms are saying the equivalent of things like "help me!" and "die!" Finding Nemo, this isn't.

At the root of these communications is a competition between corals and an algae called Chlorodesmis fastigiata. In the wild, the algae can start growing on reefs, where it is able to send a simple message to nearby coral: die. Various studies have indicated that the algae can carry coral disease and create an oxygen-depleted environment that's harmful to corals. Within three days of researchers placing the algae on a coral, the coral's photosynthetic activity dropped by about 80 percent. With the corals gone, the algae can then occupy the reef.

But, as researchers found, corals can fight back. Simply placing an extract of the seaweed near the coral caused it to emit its own message: come help me! The recipients of this message? Fish called gobies. Pairs of these fish generally occupy a nest at the base of a coral growth. But, in the authors experiments, simply exposing a bit of coral to an extract of the toxic seaweed was enough to attract most of the gobies in the area in as little as 15 minutes.

Once there, the fish got to work. Over three days, the abundance of the seaweed dropped by about 30 percent. And, more significantly, the corals recovered the majority of the metabolic activity that they had lost when the algae first appeared.

The authors tested this with two species of goby. In one case, the fish simply cleared off the algae without eating it. But a second one happily chowed down on the intruder, based on an examination of its stomach contents. The authors noted a difference between these species: the one that ate the algae also had a predator defense that involved producing a mucus that was toxic to other fish.

So, the authors tested whether eating the algae was necessary for the production of the toxic stew. It wasn't, but they did find that consuming algae increased the potency of the toxins, which was able to disorient predators twice as fast if the fish that produced it had been chewing on seaweed.

In all, the picture this research paints is a mix of symbiosis and chemical warfare. The primary combatant is the algae, which tries to off the nearby coral. That sets off a chain of mutually beneficial interactions, as the coral attracts gobies, which can find a home there and help clear off the intruder. At least one of these goby species benefits even further by increasing its own chemical warfare assault at the expense of the algae.

But not everyone is arming for battle. The researchers also tested a damselfish that lives in corals, and found that it ignores all the chemical signaling going on.

The authors point out that corals are declining rapidly around the globe, being stressed by things like pollution, rising temperatures, and ocean acidification. Efforts to preserve them may be able to benefit from a greater understanding of the full ecosystem in which corals live.

15 Reader Comments

Two items.First is it not interesting that we favor the coral here. I do not have the time interest or background to explore which is better or if there is no appropriate value judgement to be applied but you, Dr John (and myself I must admit) appear to favor the coral. Underdog? usefulness why?

Second I could not help creating a picture in this political season with your first sentence: 'There are lots of organisms that don't have a brain, but can still communicate. 'Nature Lover dba Bopper

As a marine aquarium enthusiast, I naturally find the ecosystems of coral reefs very interesting. It's a shame that they are in such danger around the globe. Unfortunately, I don't see their destruction slowing down any time soon as mankind wantonly ignores ecological concerns. One day there might be more coral ecosystems alive in aquariums like my own than in nature - that would be truly tragic.

Edit: for the record, I'm fully aware of the ecological concerns of hobbyist aquarium harvesting, and buy only captive-bred specimens. Either way, reef harvesting pales in comparison to the damage done from industrial and commercial activities.

First is it not interesting that we favor the coral here. I do not have the time interest or background to explore which is better or if there is no appropriate value judgement to be applied but you, Dr John (and myself I must admit) appear to favor the coral. Underdog? usefulness why?

While all animals compete for room, out of control alga infestations typically not only smother the corals, but destroy the entire ecosystem by removing habitat and good sources or food and shelter. Often the algae bloom then dies off itself, leaving a virtual desert that can take decades to restore since, like most ecosystems, reefs go through waves of habitation types and growth patterns. Think new scrub and shrubs versus old growth forest. Both have their place; having all scrub forest would be bad.

There are other "invasive" critters which do similar damage (like overpopulations of sea urchins), so it isn't an anti-algae bias, it's a bias against destructive monocultures.

Belross wrote:

I'm fully aware of the ecological concerns of hobbyist aquarium harvesting, and buy only captive-bred specimens.

Try raising fish or inverts sometime if the opportunity presents. It's a lot of careful work, but it will give you a new appreciation for reef life. Even something like clownfish which are fairly easy to breed in captivity if you go by the numbers are an incredible learning experience. Older kids, if you have them, may get a kick out of it, too.

NicoleI am quite aware of competition in nature, communication between lower organisms (cf http://www.princeton.edu/chemistry/facu ... d/bassler/ she at my alma mater where I got my first biochem degree ) but what my somewhat quirky view of the world was trying to say is that why do we have such a bias? Monocultures exist, they come and they go. Even destructive ones. Sentient ones??

I have a very strong emotional bias on the individual level when pseudomonas 'overpopulations' try to kill my patients but on a crude biologic level, this is life of course- fitness tests every day. I do tilt the balance both ways-longer story. These waves of destruction/reconstruction are of course very natural at several levels. Witness irruptive bird migrations, natural fires and recovery, Mount St Helen. Is it clear that the loss of coral destroys the entire ecosystem (vs an entire ecosystem)or just makes way for another?

Were it not for the fact that we have concerns for the loss of the coral ecosystems because of our behaviors would we have such biases?Just an observation that may seem weird,of a bias of little import, that struck me, that I also share, ahh never mind.

One thing that Dr Bassler's lab is doing with some of this communication data that might be more practical in our battles with nature:

Finally, we are focused on developing molecules that are structurally related to AI-2. Such molecules have potential use as anti-microbial drugs aimed at bacteria that use AI-2 quorum sensing to control virulence. Similarly, the biosynthetic enzymes involoved in AI-2 production and the AI-2 detection apparatuses are viewed as potential targets for novel anti-microbial drug design.

This might be less prone to evolutionary escape or maybe useful as an adjunct to our current approaches- eg antibiotics which have their own issues.

I believe the technical name for these kinds of signals, at least between the algae and the corals, is allelopathy. It's also the reason why pine forests tend to have less underbrush, and why certain plant species don't do well together despite doing well individually in the same conditions. There is so much about this chemical warfare between organisms, especially the kind we tend to think of as passive like plants, that we are only beginning to understand. We don't have anything approaching a complete picture for this. Biologists will be busy for a very, very long time trying to map out these networks of interaction.

Any plans for a sequel introducing to non-biologists how our immune system keeps in check the bacteria in our gut?

Lacking sufficient education in the matter I'm probably putting my foot in my mouth but it seems to me that this form of control can be categorized as chemical warfare too. Except that it appears as if it were a form of crowd control, more than an all-out war.

Two items.First is it not interesting that we favor the coral here. I do not have the time interest or background to explore which is better or if there is no appropriate value judgement to be applied but you, Dr John (and myself I must admit) appear to favor the coral. Underdog? usefulness why?

A coral reef is the only place where you can stick your head under the water and be guaranteed to see hundreds of thousands (millions?) of fish.

Reefs create an abundance of life not found anywhere else on in our solar system.

Hmm.. I wouldn't say that, but I would see this have been an on going battles among the reef, algae and corals, and what they've been doing there under the water just part of the survival technique done by all living things and as for all non-living things as well - reef, coral?

Of all the known destructive creatures on this planet, human are known for the most destructive living creatures on this planet Earth and we're also the most creative one too. We do both - by killing you and making other live a better life? Suckers! How's that for an example here?

The corals, algae and reef seems been doing their best to survive. What they do are no different what the human do above the water, sometimes under the water? <repeating myself>

(No I'm not getting into a political debate here.) :-)

So that said it all, should we be self-destructed because of we are the most dangerous living creatures on Earth?